The invention relates to a multiple-stage heat exchanger for heat treatment of fine-grained material with a hot gas stream which flows upwards through several heat exchange stages arranged one above the other. Material is supplied to the heat exchanger from above and is repeatedly separated from the gas stream and then reintroduced to the heat exchange stage immediately below. At least one of the lower heat exchange stages contains a deflector/separator having gas inlet and outlet pipes offset relative to each other on the periphery of the deflector/separator and arranged at a different height above a hopper. At least the uppermost heat exchange stage has a cyclone with a horizontal gas inlet pipe and a vertical dip pipe.
Known heat exchangers for preheating fine-grained material (for instance crude cement powder) before a burning or sintering process consist of a number of cyclones which are connected to each other via their gas and material delivery lines and are passed through successively by the material in counterflow to the hot gas. The connection of several cyclone stages one behind the other results--over the whole heat exchanger--in an almost ideal counterflow of gas and material and thus a very high degree of thermal efficiency in the transfer of heat.
The known constructions have the disadvantage that they have a relatively high energy requirement in order to overcome the great resistance to flow of the numerous cyclone stages. The considerable size, and particularly the great height, of such a multiple-stage heat exchanger is also unfavourable.
A multiple-stage heat exchanger is also known (German Auslegeschrift No. 1280486) which contains a deflector/separator in three heat exchange stages and a cyclone in the last stage. In plan view the deflector/separators have a rectangular expansion chamber with a funnel-shaped base into which an inlet channel for the hot gas stream opens on one side from below and an exhaust channel leads out upwards on the opposite side, and a delivery pipe for the material eliminated in the stage immediately above opens in the cover of the chamber.
A deflector/separator of this type has a substantially lower pressure loss than a conventional cyclone, but on the other hand it has the disadvantage of a very poor degree of separation. A further serious disadvantage of this known arrangement is that the material introduced into the deflector/separator via the cover of the expansion chamber is in contact with the hot gas stream for quite a short time before it is eliminated from the gas stream in the expansion chamber; this results in a poor degree of heat transfer.